3. The Orbit

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Describe the orbit:: Pyramidal shaped bony cavity
What 6 types of structures does the orbit contain?: -Eyeballs
-Muscles
-Nerves
-Vessels
-Fat
-Lacrimal apparatus
How are the walls of the orbit oriented?: Medial walls are parallel to each other; (0' angle)
Lateral walls perpendicular (90' angle)
What are the 4 orbit margins and what bones make up each margin?: 1. Supraorb: frontal/sprbtlnotch
2. Lateral: frontal/zygomatic
3. Infraorb: zygomatic/maxilla
4. Medial: maxilla + frontal
What composes the orbit roof and what is its special feature?: -Orbital plate of frontal bone
-Lacrimal fossa for lacrimal gland
What composes the orbit lateral wall and what is its special feature?: -Zygomatic bone + greater wing of sphenoid
-Features the superior orbital fissure
what two compartments communicate via the sup orb fissure?: Orbit + middle cranial fossa
What passes through superior orbital fissure?: CNs 3,4,V1,6
Opthalmic vein
What does the orbit floor consist of?: Orbital plate of maxilla
What 2 features in the orbit floor are noteworthy?: -Inferior orbital fissure
-Infraorbital groove
What bone has the following: -Superior orb fissure -Inferior orb fissure: Sup = ethmoid

Inf = maxilla (NOT sphenoid)
What does the inferior orbital fissure allow to communicate?: Orbit + pterygopalatine fossa and infratemporal fossa
What passes through the inferior orbital fissure?: -V2 maxillary nerve
-Inferior opthalmic vein (going to the pterygoid plexus)
What passes through the infraorbital groove?: V2 branch - infraorbital nerve
Components of medial orbit wall: (4): -Maxilla
-Lacrimal bone
-Orbital plate of ethmoid
-Body of sphenoid
Features of medial orbit wall (2):: -Lacrimal groove
-Optic canal
What lies in lacrimal groove?: Lacrimal sac
What bone contains optic canal, what does it allow commun. w/?: -Sphenoid bone
-Communcn w/ mid cranial fossa
What passes thru Optic canal:: Optic nerve - CN II
opthalmic artery
What is the opening between the eyelids called?: Palpebral fissure
What are the corners of the eyes called?: Angles (canthi) - med/lat
What glands are in the eyelids skin?: Ciliary - sweat/sebaceous
4 Eyelid muscles:: -Orbicularis oculi
-Submusc. connectv tissue - contin w/ galea aponeurotica.
-Levator palpebrae superioris
-Superior tarsal
Action of levator palebrae:: voluntarily raises upper eyelid - deep fibers insert into superior tarsal plate.
Superior tarsal muscle action:: Smooth muscle; widens eyes to their fullest extent via sympathetic innervation.
Function of glands in the tarsal plates:: Secrete oily substance over tear layer; causes tears to spill over when eyes fill.
What is the orbital septum?: Membranous sheet connecting tarsal plates to orbital rim; continuous w/ periosteum.
4 Main points re: conjunctiva:: 1. Transparent mucous membrane
2. Palpebral (inner eyelids)
3. Bulbar (over eyeball)
4. Fornix (crease betwn above 2)
6 Main parts of the Eyeball:: 1. Lens
2. Anterior cavity
3. Posterior cavity
4. Fibrous tunic
5. Vascular tunic
6. Neural/Retinal layer
Basic structure of the lens:: Transparent, biconvex;
Tightly packed lens fibers;
Lens capsule = basement membrane surrounding fibers.
What special structures facilitate change in lens shape during accommodation?: Zonule fibers - parasympathetic innervation
What common clinical problem occurs with the lens?: Cataracts
Where is Anterior cavity located; what does it contain?: -In front of lens
-Contains aqueous humor
2 main areas of the anterior cavity:: 1. Anterior chamber
2. Posterior chamber
Where is the anterior chamber?: Between posterior surface of cornea, and anterior surface of lens/iris.
Where is the posterior chamber?: Between posterior surface of iris/lens, and suspensory ligament.
Where is the posterior CAVITY?: behind the lens
What does the posterior cavity contain?: Vitreous humor
What are the 2 components of the fibrous tunic?: 1. Sclera (back 5/6)
2. Cornea (front 1/6)
Main functions of the sclera:: -Maintains eyeball shape
-Insertion of extraocular muscles
Main functions of cornea:: -Refraction
(transparent/avascular)
3 structures found in the vascular tunic:: 1. Choroid
2. Ciliary body
3. Iris
What is the choroid?: -Dense capillary plexus w/ pigment cells
Where is the choroid found?: Between sclera/retina
What is the ciliary body?: The layer of the vascular tunic that produces aqueous humor and contains the ciliary muscle.
What is the purpose of aqueous humor?: provides nutrients to the avascular lens and cornea
Where does aqueous humor from the ciliary body go?: Passes through the pupil, drains into the venous sinus at the iridocorneal angle.
What common clinical problem is associated with the ciliary body and aqueous humor?: glaucoma
How is the ciliary muscle connected to the lens?: By zonule fibers.
What type of muscle is the ciliary m?: smooth muscle like a sphincter
What does the ciliary muscle do?: Controls the shape of lens.
How exactly does the ciliary m work?: 1. Parasymp nerves stim it
2. Contraction decreases tension of zonule fibers
3. Lens curvature increases -> now u can see close up
What is the iris?: A highly pigmented diaphragm extending over the anterior lens surface.
What is the pupil?: The hole in the middle of iris
What 2 muscles control the iris? What kind of nerves innervate each?: -Sphincter pupillae; parasymp
-Dilator pupillae; sympathetic
What 2 types of layers make up the retina?: 1. Retinal pigment epithelium
2. Nerve fiber layer - forms optic nerve.
What are the 4 key components of the lacrimal apparatus?: 1. Gland
2. Puncta
3. Sac
4. Nasolacrimal duct
Where is the lacrimal gland and how is it situated there?: -Superolateral orbit angle
-Levator palpebrae superioris aponeurosis splits gland into: -Orbital part (in lacrimal fossa of zygomatic bone)
-Palpebral part (lateral upper eyelid)
Where does the lacrimal duct open into?: Fornix
Where does lacrimal fluid flow?: From lateral upper fornix to lower medial Lacrimal Lake.
What are lacrimal puncta?: Small apertures withn lacrimal papillae elevations along each eyelid.
Where does lacrimal fluid flow after entering lacrimal puncta?: Into lacrimal canaliculi -> lacrimal sac
What and where is the lacrimal sac?: In the lacrimal fossa of the lacrimal bone; the opening of the nasolacrimal duct.
Where does the nasolacrimal duct flow into?: The inferior nasal meatus.
What 2 major arteries feed the orbital region?: 1. Internal carotid
2. External carotid
What branch does the internal carotid send to the orbit?: Opthalmic artery via optic canal
What are the 6 main branches of the Opthalmic Artery?: 1. Central artery of retina
2. Lacrimal artery
3. Supraorbital artery
4. Supratrochlear artery
5. Dorsal nasal artery
6. Post/ant ethmoidal aa.
Where does the central artery of retina run?: Within dural sheath of optic nerve's inferior surface; supplies the retina.
Where does the lacrimal artery go and feed?: To the lacrimal gland, conjunctiva and eyelids -> becomes the lateral palpebral artery.
What happens to the lacrimal artery ultimately?: Anastomoses w/ the zygomatic-orbital a. and facial artery (of external carotid)
What does the Supraorbital artery supply?: -Superior rectus m
-Levator palpebrae superioris
Where does the supraorbital a ultimately end up?: Passes thru supraorbital notch to feed 6 things:
-forehead and scalp
-medial canthus
-diploe of frontal bone
-periosteum & frontal sinus
What is the supratrochlear artery and what does it feed?: Terminal branch of opthalmic artery; feeds forehead/scalp and pericranium.
What is important about the dorsal nasal artery?: -Supplies lacrimal sac and skin of the nose.
-Anastomoses with external carotid via infraorbital artery.
What 3 branches to the orbit come from the external carotid?: 1. Infraorbital artery
2. Zygomatico-orbital artery
3. Facial artery
What is the infraorbital artery a branch of?: Maxillary
What 3 things does infraorbital artery supply?: 1. Inferior rectus m
2. Inferior oblique
3. Lacrimal sac
What does the infraorbital a anastomose with?: Dorsal nasal artery of internal carotid's opthalmic artery. Also the facial artery.
What is the zygomatico-orbital artery a branch of? What does it supply?: The superficial temporal artery.
-Supplies orbicularis oculi muscle.
What does the zygomaticorbital artery anastomose with?: Lacrimal artery (from opthalmic artery)
What does the facial artery anastomose with?: -Dorsal nasal artery
-Infraorbital artery
What 3 arteries does the transverse facial artery anastomose with?: 1. Facial
2. Infraorbital
3. Lacrimal
What are the 3 important veins of the orbit?: 1. Central vein of the retina
2. Superior opthalmic vein
3. Inferior opthalmic vein
Where does the central vein of the retina run/drain?: With the optic nerve; drains into cavernous sinus or superior opthalmic vein.
What does the superior opthalmic vein communicate w/?: -Facial vein
-Supraorbital vein
What hole does the superior opthalmic v. pass through and where does it drain?: Passes through superior orbital fissure to drain into cavernous sinus.
What does the inferior opthalmic vein receive blood from?: Inferior/medial parts of the orbit.
What does the inferior opthalmic vein connect to and drain into?: -Connects w/ superior opthalmic vein and/or drains via inferior orbital fissure into pterygoid plexus.
What 2 sensory nerves carry optic information?: 1. CN II - Optic
2. CN V1 - Opthalmic
What functional modality is attributed to each optic sensory nerve?: Optic = special somatic afferent

Opthalmic = general somatic afferent
How does the optic nerve begin?: -Axons of retinal ganglion cells form a nerve
-Nerve pierces sclera medial to posterior pole of eyeball
What covers the optic nerve?: Meninges and CSF
What hole does the optic nerve run through and where does it go?: -Courses through optic canal of sphenoid bone
-Forms optic chiasm
-Tracts terminate in lateral geniculate nucleus.
Where does the opthalmic nerve (V1) arise from?: Sensory receptors which transmit info via peripheral processes.
What hole does the opthalmic nerve course through, and where does it go after that?: -Superior orbital fissure
-Through cavernous sinus to NCB's in trigeminal ganglion.
What happens to CN V1 (opthalmic) at the trigeminal ganglion?: Its central nerve processes transmit sensation to 2 things: 1. Principle sensory nucleus
2. Spinal nucleus
what are the 3 very important branches of the opthalmic nerve?: 1. Lacrimal nerve
2. Frontal nerve
3. Nasociliary nerve
what are the 3 branches of the Frontal nerve (of CN V1)?: 1. Supratrochlear
2. Supraorbital
3. Nerve to the frontal sinus
What are the 5 branches of the Nasociliary nerve?: 1. Anterior/posterior ethmoidal nerves
2. Infratrochlear nerve
3. Meningeal nerve
4. Long ciliary nerves
5. Short ciliary nerves
What 3 nerves give motor innervation to the orbit?: 1. CN III - Oculomotor
2. CN IV - Trochlear
3. CN VI - Abducent
What type of functional modality are the 3 orbit motor nerves?: General somatic efferent
Where do the axons of CN III arise?: From neurons in midbrain oculomotor nucleus
-Located near median plane, at the midbrain-pons junction.
What is the route of CN III in going from the oculomotor nucleus to the eye muscles?: -Passes between posterior cerebral and superior cerebellar arteries
-Passes thru cavernous sinus
-Thru Superior orbital fissure
-Within common tendinous ring
What are the 2 divisions formed from the oculomotor nerve?: 1. Superior
2. Inferior
What is innervated by the Superior Oculomotor Nerve? (2 things): 1. Levator Palpebrae superioris
2. Superior rectus
What is innervated by the Inferior Oculomotor Nerve? (3 things): 1. Medial rectus
2. Inferior rectus
3. Inferior oblique
What does the trochlear nerve innervate?: Superior oblique
What is unique about the trochlear nerve?: Axons originate from nuclei in the DORSAL brainstem surface.
How does the trochlear nerve get to the orbit?: Thru cavernous sinus, then thru Superior Orbital Fissure
How does the Abducent nerve get to the orbit?: Same way that the trochlear does, except from ventral brainstem side.
What orbit structures receive autonomic innervation? Which get parasympathetic and which get sympathetic?: Lacrimal gland = both
Sphincter pupillae - para
Ciliary muscle - para
Dilator pupillae = sympathetic
Superior tarsal = sympathetic
What is the 2 neuron system like -For parasympathetic neurons? -For sympathetic neurons?: PARA: long preganglionic + short post-ganglionic neuron
SYMP: short preganglionic + long postganglionic neuron.
Where are the preganglionic parasympathetic NCBs for the lacrimal gland located?: In the superior salivatory nucleus
How do the preganglionic parasymp fibers for lacrimal gland get to it?: -Emerge from brain w/ Nervous Intermedius (CN VII)
-Pass thru geniculate ganglion
-Continue as Greater Petrosal -Join Deep Petrosal nerve
What do the Greater Petrosal + Deep Petrosal nerves combine to form?: Nerve of the Pterygoid Canal
Where do the preganglionic parasymp fibers for the lacrimal gland synapse?: At the Pterygopalatine ganglion
How do postganglionic parasymp fibers from the Pterygopalatine ganglion get to the Lacrimal gland?: -Travel w/ Zygomaticotemporal nerve + Lacrimal nerve
What happens once parasymp nerves get to the Lacrimal gland?: They stimulate secretion.
What happens when SYMPATHETIC nerves get to the lacrimal gland?: They stimulate Vasoconstriction of blood vessels.
Where are the preganglionic SYMPATHETIC NCB's for the lacrimal gland?: In the lateral horn of the spinal cord gray matter - just like for all other sympathetic preganglionic neurons.
Where do preganglionic sympathetic lacrimal fibers synapse?: Superior Cervical Ganglion
What structure is formed by postganglionic sympathetic lacrimal fibers?: Internal Carotid nerve
How does the internal carotid sympathetic nerve get to the lacrimal gland?: Travels w/ Deep Petrosal nerve; Joins Greater Petrosal nerve;
Travels w/ Nerve of Pterygoid Canal
So how do both sympathetic AND parasympathetic postganglionic nerve fibers get to the lacrimal gland?: By traveling with the Zygomaticotemporal and Lacrimal nerves.
What type of innervation do Sphincter pupillae and ciliary muscles receive?: Parasympathetic
Where do preganglionic parasymp fibers for Sphinct. pupillae and ciliary muscles arise? How do they get where they're going?: From Edinger-Westphal nucleus in midbrain; travel w/ CN III to the ciliary ganglion.
What happens to parasymp preganglionic fibers at the ciliary ganglion?: Synpase and send postganglionic fibers via SHORT CILIARY NERVES (V1 branches) to Sphincter pupillae and ciliary mm.
What happens when the postganglionic parasymp fibers of Short Ciliary Nerves reach their muscles?: -Pupil constriction
-Lens thickening (accommodation)
What type of innervation do Dilator pupillae and Superior tarsal muscles receive?: Sympathetic
Where do preganglionic symp fibers for Dilator pupillae and Superior tarsal muscles arise? How do they get where they're going?: From spinal cord; enter the sympathetic trunk and synapse in Superior Cervical Ganglion.
What happens to postganglionic sympathetic fibers for Dilator pupillae and Superior tarsal muscles?: Form Internal Carotid nerve plexus; pass uninterrupted thru ciliary ganglion.
What V1 branch carries sympathetic innervation to Dilator pupillae and Superior tarsal muscles after passing thru the ciliary ganglion?: Long Ciliary nerves (V1)
What happens when sympathic nerves stimulate Dilator pupillae and Superior tarsal muscles: -Pupils widen
-Palpebral fissure widens all the way.
What are the 3 AXES of the eye?: 1. Vertical
2. Horizontal/transverse
3. Anteroposterior
What 3 actions occur around the vertical axis?: 1. Abduction
2. Neutral
3. Adduction
What 3 actions occur around the horizontal axis?: 1. Elevation
2. Neutral
3. Depression
What 3 actions occur around the anteroposterior axis?: 1. Extorsion
2. Neutral
3. Intorsion
What is extorsion? What is intorsion?: Extorsion: 12 o'clock on eye twists laterotemporally.
Intorsion: 12 o'clock on eye twists medionasally.
Levator palpebrae superioris: -Innervation -Action: Innervation: CN III
Action: raises the eyelid
Medial rectus: -Innervation -Action around axes: Innervation: CN III
Vertical axis: adduction
Horizontal ax: nothing
Antpost axis: nothing
Lateral rectus: -Innervation -Action around axes: Innervation: CN VI
Vertical axis: abduction
Horizontal ax: nothing
Antpost axis: nothing
Superior rectus: -Innervation -Action around axes: Innervation: CN III
Vertical axis: adduction(2')
Horizontal ax: Elevation (1')
Antpost axis: Intorsion (3')
Inferior rectus: -Innervation -Action around axes: Innervation: CN III
Vertical axis: adduction(2')
Horizontal ax: Depression(1')
Antpost axis: Extorsion (3')
Superior oblique -Innervation -Action around axes: Innervation: CN IV
Vertical axis: abduction
Horizontal ax: Depression
Antpost axis: Intorsion
Inferior oblique -Innervation -Action around axes: Innervation: CN III
Vertical axis: abduction
Horizontal ax: Elevation
Antpost axis: Extorsion
Why does SO cause depression around horizontal axis?: Because it elevates the posterior aspect of the eye
Why does IO cause elevation around the horizontal axis?: Because it depresses the post aspect of eye.
Which muscles achieve eye movement in the horizontal plane only?: Medial and lateral rectus mm.
What muscles achieve eye elevation or depression?: Superior oblique
Inferior oblique
Superior rectus
Inferior rectus
What 2 conditions regarding the axis of gaze are achieved by eye ABDUCTION?: 1. Axis aligned w/ long axis of rectus muscles
2. Axis perpendicular to long axis of oblique muscles.
What is achieved by abducting the eye?: -Rectus muscles are optimally positioned to elevate or depress
-Oblique muscle contribution is minimal
What 2 conditions regarding the axis of gaze are achieved by eye ADDUCTION?: 1. Axis perpendicular to long axis of rectus muscles
2. Axis aligned w/ long axis of oblique muscles
What is achieved by adducting the eye?: -Rectus muscles contribute minimally
-Oblique muscles optimally positioned to elevate/depress
What mnemonic is useful for remembering what direction to tell the patient to look when testing extraocular muscles?: O's toward the nose and upside down.
What is a common clinical complaint seen in eye motor nerve injuries?: Diplopia - double vision.
What 2 general types of neural problems can cause diplopia?: -Central lesions - in brainstem nuclei
-Peripheral lesions - injuries to the nerves.
What is ptosis? What is lateral strabismus?: Ptosis = drooping eyelid
Lat Strabismus = eye turning down and laterally
Damage to what nerve causes ptosis, and why?: CN III - because the levator palpebrae superioris is paralyzed.
Why does lateral strabismus occur in CN III damage?: Medial rectus and Superior rectus muscles are paralysed; leaves LR6(SO)4 unopposed.
What are 4 possible casues of CN III injury?: -Intracranial aneurysm
-Trauma
-Inflammation (syphilis, diabetic neuropathy)
-Cavernous sinus thrombosis
What will a CN IV lesion result in?: Inability to look down and nasally (depress/adduct)
Why is depress/adduction inhibited by CN IV lesion?: Superior Oblique is paralysed
What is a clinical sign of CN IV injury?: Head tilt - toward opposite side of eye injured
Why do patients w/ injured CN IV tilt their head?: Because the normal eye intorts, realigning the axis of gaze with the extorted injured eye.
What are 2 common causes of CN IV injury?: -Trauma
-Cavernous sinus thrombosis
What is a common sign of CN VI injury? Why?: Medial strabismus - medial rectus m is unopposed b/c lateral rectus is paralyzed
What is the most common cause of CN VI injury?: Cavernous sinus thrombosis
What nerve injury would result in a loss of lacrimation?: CN VII - w/ greater petrosal nerve involved too.
What nerve is associated with Horner's syndrome?: CN III sympathetic fibers
What are 4 symptoms of Horner's Syndrome?: -Miosis (pupil constriction)
-Ptosis (drooping eyelids)
-Anhydrosis (lack sweating)
-Erythematosis (skin blushes)
What causes miosis in horner's syndrome?: Dilator pupillae paralysis - unopposed sphincter pupillae
What causes ptosis in horner's syndrome?: Paralysis of superior tarsal m
What causes anhydrosis in horner's syndrome?: Loss of head/neck sweat gland innervation
What causes erythematosis in horners syndrome?: Blood vessel dilation
What 2 conditions can result from CN III parasymp fiber lesion?: -Loss of accommodation to light reflex
-Pupil dilation
Why do pupils dilate in CN III Parasymp fiber lesions?: Sphincter pupillae muscles are paralysed so dilator pupillae m are unopposed.
Why is accomodation to light reflex impaired by CN III lesion?: B/c the ciliary m and sphincter m are paralyzed.

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